Polycarbonates are a well known class of high impact resistant thermoplastic resins characterized by optical clarity, high ductility as well as other advantageous properties. They are frequently employed as lenses and windows as a result of their transparency. Bisphenol A polycarbonate (BPA) is the predominant commercially available resin of this type. It is derived from 2,2-bis(4-hydroxyphenyl)propane, and ordinarily has a glass transition temperature of about 150.degree. C.
It is of increasing interest to prepare polycarbonates which, while retaining the heat resistance of bisphenol A polycarbonates, have higher ductility and are therefore more resistant to damage when handled. Moreover, there is need for polycarbonates which possess flame retardant properties since they are, for instance, conventionally used in the automotive and computer industries. Several flame retardant agents have been utilized in an attempt to produce flame retardant polycarbonates. For example, alkali metal salts of strong sulfonic acids are commonly used. However, when incorporated into the polycarbonate, the resulting polymer is hydrolyrically sensitive. Further, when using these salts, it is also necessary to employ drip inhibitors or gas phase flame retardant agents. This is not ideal since drip inhibitors destroy the clarity of the polymer and gas phase retardants are often halogenated which creates problems with corrosion and toxicity. As an alternative to the above, phosphorus containing compounds such as triphenylphosphate have been used. When blended with a base polycarbonate, some flame retardant properties are observed. However, the resulting polymer blends are not desirable since they possess low glass transition temperatures (Tg) and low impact resistance when compared to the base resin.
Accordingly, the instant invention is directed to novel polycarbonate compositions. Said polycarbonate compositions contain copolymers of aromatic polycarbonates and they unexpectedly display high glass transition temperatures, high impact resistances, flame retardant properties as well as superior brittle ductile transition temperatures.